1. Field of the Invention
The present invention relates to pharmaceutical formulations involving the inclusion of an active pharmaceutical ingredient (“API”) in a pharmaceutically-acceptable single crystal matrix. More particularly, the crystals contain growth-sector specific, oriented inclusions of active pharmaceutical ingredients which are isolated. The active pharmaceutical ingredients have higher stability and shelf-life, and can be delivered in conventional dosage forms. This invention has general application to active pharmaceutical ingredients, and in one aspect has particular application to biopharmaceuticals. As used herein, the term “biopharmaceuticals” is used to refer to a subset of API's which are polymeric in nature, including for example, proteins, polypeptides, enzymes, immunoglobulins, polynucleic acids, and plasmids.
2. Description of the Prior Art
There is a continuing need for pharmaceutical compositions which are capable of maintaining the quality and efficacy of the API during storage and delivery. The loss of potency of an API is a critical concern in assuring that viable, effective drugs are delivered to patients. It is similarly desirable to have formulations which do not require special package or handling. Further, it remains a constant goal to provide active pharmaceutical ingredients in a form which facilitates their use by the consumer, such as though convenient dosage forms. The present invention addresses these and other issues concerning pharmaceutical compositions and formulations.
Although not limited to biopharmaceuticals, the usefulness of the present invention is well exemplified with respect to biopharmaceuticals, many of which demonstrate the problems encountered in prior-art approaches. Ensuring long-term stability and maintaining activity of biopharmaceuticals is a prevalent concern. The chemical complexity and conformational fragility of protein drugs, for example, make them highly susceptible to both physical and chemical instabilities and threaten their emergence into the marketplace. Denaturation, adsorption with container walls, aggregation, and precipitation can result from non-covalent interactions between a drug and its environment. Insulin, for instance, has been shown to adsorb onto the surfaces of glass and plastic containers, and to have interactions at air-water interfaces, leading to denaturation, aggregation and precipitation. For example, upon demonstration human growth hormone (HGH) forms dimers and higher molecular weight aggregates, and glucagon in solution has been shown to readily gel or aggregate when subjected to mechanical stress.
As a further example, researchers have distinguished nine major reaction mechanism by which proteins degrade, including hydrolysis, imide formation, deamidation, isomerization, racemization, diketopiperazine formation, oxidation, disulfide exchange, and photodecomposition. The rates of these deleterious processes depend in large measure on the protein and its environment. The primary chemical degradation products of glucagon, for example, include oxidation of Met (27), deamidation of Gln (24), and acid-catalyzed hydrolysis at Asp (9), Asp (15) and Asp (21). HGH undergoes chemical decomposition via oxidation at Met (14) and deamidation at Asn (149).
A critical challenge of product development science in the pharmaceutical industry therefore has been devising formulations that maintain the stability of the active pharmaceutical ingredient over an acceptable shelf-life. This has been especially difficult to achieve for certain API's which are unstable in solution or with respect to many common formulation processes. Developing techniques for stabilization and storage looms as a great impediment to the pharmaceutical industry. Formulation scientists have consequently used a variety of techniques to enhance the stability of API's while maintaining other important product characteristics such as biocompatibility, absorption, pharmacokinetics, efficacy and excretion.
One technique used in formulating biopharmaceuticals has been lyophilization of the biopharmaceutical solution in the presence of excipients, buffers and/or bulking agents. However, even lyophilized preparations must typically be stored under refrigeration, a requirement which is neither technically nor economically feasible in many markets and inhibits flexibility of patient use. There has therefore been a continuing demand for formulations of many biopharmaceuticals which would permit their storage at ambient temperatures. This would permit more rapid development of products, increasing flexibility in shipping, storing and carrying the drug products, and allowing introduction and use of such products in markets where refrigeration is too costly. Moreover, the increased stabilization of biopharmaceuticals would naturally improve the general use of the biopharmaceuticals where shelf life is an important consideration, whether or not refrigeration or other concerns are at issue.
The prior art use of excipients in the lyophilization of biopharmaceuticals has been directed away from inclusion of the biopharmaceuticals in single crystals in the manner of the present invention. It has been widely assumed that amorphous glasses are critical in the stabilization of biopharmaceuticals by such excipients in lyophilized form, and it has been suggested that the drug molecules must exist in amorphous regions between the crystalline domains. See, e.g., M. J. Pikal, “Freeze Drying of Proteins”, to be published in Peptide and Protein Delivery, 2nd Ed., V. H., L. Lee, Marcel Dekker, Prepint, 1995. Implicit in this reasoning is the conclusion that the biopharmaceuticals could not exist as guests within single crystals.
In the process of lyophilization, typically an aqueous solution containing a biopharmaceutical with a limited amount of excipient(s) is frozen and then dried under vacuum to produce solids of sufficient stability for storage and distribution. Excipients are added to prevent blow out of the product, to provide stability during lyophilization and/or dissolution, and to enhance compatibility for parenteral use. Various excipients used with lyophilization have included salts, metal ions, polyalcohols, surfactants, reducing agents, chelating agents, other proteins, amino acids, fatty acids, and phospholipids. The more frequently used excipient include mannitol, alanine, glycine, sorbitol, lactose, arginine, and maltose. The results obtained with such excipients, however, have usually been inconsistent. Most lyophilized biopharmaceuticals are amorphous powders that have not specific structure, and as a result, the amount and location of the incorporated biopharmaceutical varies widely for the product particles. Also, they are typically readily dissolved, rendering them unsuitable for use as a sustained-release material. Further, there is no isolation of the pharmaceutical molecules from the environment or one another, leaving them susceptible to degradation by various mechanisms. Studies have shown that lyophilization of excipients can typically damage proteins rather than protect them. See, e.g., J. F. Carpenter, J. H. Crowe, “Infrared spectroscopic studies of the interaction of carbohydrates with dried proteins”, Biochemistry 1989, 28, 3916–3922; J. F. Carpenter, S. Prestrelski, T. Arakawa, “Separation of freezing- and drying-induced denaturation of lyophilized proteins by stress-specific stabilization: I. Enzyme activity and calorimetric studies,” Arch. Biochem. Biophys. 1993, 303, 456–464. K. Izutsu, S. Yoshioka, Y. Takeda, “The effects of additives on the stability of freeze-dried β-galactosidase stored at elevated temperatures”, Int. J. Pharm. 1991, 71, 137–146. K. Izutsu, S. Yoshioka, T. Teroa, “Decreased protein-stabilizing effects of cryoprotectants due to crystallization”, Pharm. Res. 1993, 10, 1232–1237.
Crystallized pharmaceuticals have been used in some instances, but there have been inherent limitations. Some API's, e.g. insulin, can be crystallized themselves, and are useful in that form for administration to patients. However, the majority of biopharmaceuticals either do not crystallize or the crystallization is very difficult, particularly on a commercial scale. Further, crystallization procedures are limited to the use of pharmaceutically-acceptable ingredients and process conditions that do not adversely affect the active pharmaceutical ingredient, thus further constraining the ability to obtain desired microcrystalline suspensions.
The fact that macromolecules are routinely isolated in sub-millimolar concentrations in a variety of crystals is known. See, e.g., K. Strupat, M. Karas, F. Hillenkamp, Int. J. Mass Spec. Ion Proc., 111, 89–102, 1991. Also, certain aromatic acids have been employed as hosts for biopolymer guests in crystals for use in matrix-assisted laser desorption ionization (MALDI) mass spectrometry, but not for the purposes of the present invention. See, Review by F. Hillenkamp, M. Karas, R. C. Beavis, B. T. Chait, Anal. Chem, 63, 1193A–1203A; S. Borman, Chem. Eng. News, 23–25, Jun. 19, 1995. However, crystallization conditions in these studies were optimized for characterization of the incorporated biopolymers. There were no investigations into optimizations that would be relevant to pharmaceutical preparations or operations such as homogeneity of the concentration of the inclusions, process scale-up, process robustness, chemical and physical stability of the preparations, suspendability in biocompatible solutions, preservative requirements and compatibility, container/closure system compatibility, and pharmacokinetic profiles.
The difficulty in obtaining suitable single crystals of some biopolymers has encouraged structural chemists to partially orient such molecules with electric, magnetic, or flow fields, by dissolution in liquid crystals or stretched gels, and as monolayers. In a similar effort, the isolation of biopolymers in a single crystal matrix has recently been studied in an effort to use such crystals for structural analysis of the biopolymers. Such isolation technique is described in “Single Crystal Matrix Isolation of Biopolymers,” J. Chmielewski, J. J. Lewis, S. Lovell, R. Zutshi, P. Savickas, C. A. Mitchell, J. A. Subramony, and B. Kahr, J. Am. Chem. Soc. 1997, 119, 10565–10566. However, this article simply demonstrates that certain biopolymers are oriented by the host lattice, and the article suggests the use of such crystals for analyzing spectral anisotropies in biological molecules which could not otherwise be crystallized. This article does not discuss or suggest the use of this technique for enhancement of stability or sustained release of pharmaceuticals, or their administration to patients. Further, the proteins studied were not a pharmaceutical interest, the crystal materials described in this article, namely phthalic acid, gentistic acid and sinapic acid, were not selected or evaluated for biocompatibility, and the crystal sizes were not optimized for particular routes of administration. Therefore, the produced crystals with included biopolymers would not be suitable for administration to patients.
Other prior art procedures have required the use of polymers that are difficult to prepare, require harsh preparation conditions that can be harmful to the API's, and yield inconsistent results. For example, U.S. Pat. No. 5,075,291 describes a process for preparing a uniformly-dispersed, pharmaceutically-active material in a crystalline sugar alcohol matrix. However, this process requires the addition of the API into a molten sugar alcohol with considerable mechanical agitation. Many API's and virtually all biopharmaceuticals would not be stable in the extreme temperature of 110° C. and the physical stresses of a high-shear vortex mixer used for agitation. The present invention does not require these extremes of temperature and physical agitation. Also, the process of the present invention slowly includes the API into the growing crystal lattice in specific growth sectors, instead of homogeneous mixing and entrapping of the active pharmaceutical ingredient in a viscous melt.